Secreted extracellular vesicles, which include microparticles (MPs) from monocytes, are able to transfer lipids, proteins, and nucleic acids throughout the body. Procoagulant MPs produced by macrophages, their precursor monocytes, and platelets are abundant in the circulation of cART-treated HIV-infected patients. MPs are known to accumulate within the leading edge of the developing thrombus. MPs are generated from activated and dying cells as heterogeneous populations of cell-derived vesicles ranging in size from 100 nm to 1 m in diameter, and circulate in blood at concentrations of greater than 109/mL. We posit that HIV infection, under suppressive antiretroviral therapy, triggers a continuous sequence of cellular events in which the adjacent elements are closely related; yet the extremes (such as thrombosis) are quite distinct ? particularly if driven by abusive conditions. In this model, we propose that the activation of monocytes/macrophages, during HIV-infection leads to enhanced production of phosphatidylserine (PS) and tissue factor (TF)-positive MPs. Since, our own findings suggest that the activated macrophages also express the ? opioid receptor and the ? opioid peptide dynorphin A 1-17 plus the opioid receptor mRNA has been detected on macrophages, we further propose that the additional exposure to ? and opioids will regulate the size and number of resulting MPs released from these cells. This will be followed by engagement of PS on MPs by Factors Va/IXa, and by opiates as substantiated previously by the ability of morphine and other morphinans to bind stereoselectively to PS. The Specific Aims to be tested are 1) Determining the properties and prothrombinase activity of monocyte-specific MPs derived from cART-treated HIV+ subjects and healthy HIV- controls; 2) Determining if MPs will bind Factors IXa (FIXa), Factor Va (FVa), and morphine including in vivo validation that MPs will bind and transport morphine and to determine if the properties of MPs are altered by monocyte exposure to opioids. Ultimately, we will determine if there is a direct role for the increased number of MPs in cART-treated HIV+ individuals in contributing directly to the elevated rates of thrombosis observed with HIV+ patients.